Trojan Turns to Google Docs to Communicate With Command and Control

Symantec researchers have discovered a piece of malware that leverages Google Docs to communicate with its command-and-control (C&C) server.

The malware is a version of the Makadocs Trojan, which opens a backdoor on the compromised computer and tries to steal information. The latest version of the malware uses Google Docs are a proxy server to reach its C&C.

“Google docs has a function called viewer that retrieves the resources of another URL and displays it,” blogged Takashi Katsuki of Symantec. “Basically, this functionality allows a user to view a variety of file types in the browser. In violation of Google’s policies, Backdoor.Makadocs uses this function to access its C&C server.”

“It is possible that the malware author has implemented this functionality in an attempt to prevent the direct connection to the C&C from being discovered,” the researcher continued. “The connection to the Google docs server is encrypted using HTTPS, thereby making it difficult to be blocked locally. It is possible for Google to prevent this connection by using a firewall.”

This is far from the first time hackers have used non-traditional methods of communicating with their command and control infrastructure. Other pieces of malware have used Twitter and Facebook to receive instructions.

According to Symantec, Makadocs hits users as a rich text format (RTF) file or Microsoft Word document. The malicious file does not use any vulnerability in order to drop its component; instead it relies on social engineering, Katsuki wrote. He explained that its attempts to lure the user into executing it with the title and content of the document, and that clues in the code lead him to believe the malware is primarily targeting people living in Brazil.

The malware includes code to detect the operating system being used by the victim, including Windows 8 and Windows Server 2012.

“This is not necessarily a surprise for security researchers as we always encounter new malware when new products are released,” Katsuki wrote. “However, this malware does not use any particular function unique to Windows 8 and we know that this malware existed before the launch of Windows 8. Based on these facts, we believe this code must be an update to the malware.”